ceph: remove fragile __map_osds optimization

We used to try to avoid freeing and then reallocating the osd
struct.  This is a bit fragile due to potential interactions with
other references (beyond o_requests), and may be the cause of
this crash:

[120633.442358] BUG: unable to handle kernel NULL pointer dereference at (null)
[120633.443292] IP: [<ffffffff812549b6>] rb_erase+0x11d/0x277
[120633.443292] PGD f7ff3067 PUD f7f53067 PMD 0
[120633.443292] Oops: 0000 [#1] PREEMPT SMP
[120633.443292] last sysfs file: /sys/kernel/uevent_seqnum
[120633.443292] CPU 1
[120633.443292] Modules linked in: ceph fan ac battery psmouse ehci_hcd ide_pci_generic ohci_hcd thermal processor button
[120633.443292] Pid: 3023, comm: ceph-msgr/1 Not tainted 2.6.32-rc2 #12 H8SSL
[120633.443292] RIP: 0010:[<ffffffff812549b6>]  [<ffffffff812549b6>] rb_erase+0x11d/0x277
[120633.443292] RSP: 0018:ffff8800f7b13a50  EFLAGS: 00010246
[120633.443292] RAX: ffff880022907819 RBX: ffff880022907818 RCX: 0000000000000000
[120633.443292] RDX: ffff8800f7b13a80 RSI: ffff8800f587eb48 RDI: 0000000000000000
[120633.443292] RBP: ffff8800f7b13a60 R08: 0000000000000000 R09: 0000000000000004
[120633.443292] R10: 0000000000000000 R11: ffff8800c4441000 R12: ffff8800f587eb48
[120633.443292] R13: ffff8800f58eaa00 R14: ffff8800f413c000 R15: 0000000000000001
[120633.443292] FS:  00007fbef6e226e0(0000) GS:ffff880009200000(0000) knlGS:0000000000000000
[120633.443292] CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
[120633.443292] CR2: 0000000000000000 CR3: 00000000f7c53000 CR4: 00000000000006e0
[120633.443292] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[120633.443292] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[120633.443292] Process ceph-msgr/1 (pid: 3023, threadinfo ffff8800f7b12000, task ffff8800f5858b40)
[120633.443292] Stack:
[120633.443292]  ffff8800f413c000 ffff8800f587e9c0 ffff8800f7b13a80 ffffffffa0098a86
[120633.443292] <0> 00000000000006f1 0000000000000000 ffff8800f7b13af0 ffffffffa009959b
[120633.443292] <0> ffff8800f413c000 ffff880022a68400 ffff880022a68400 ffff8800f587e9c0
[120633.443292] Call Trace:
[120633.443292]  [<ffffffffa0098a86>] __remove_osd+0x4d/0xbc [ceph]
[120633.443292]  [<ffffffffa009959b>] __map_osds+0x199/0x4fa [ceph]
[120633.443292]  [<ffffffffa00999f4>] ? __send_request+0xf8/0x186 [ceph]
[120633.443292]  [<ffffffffa0099beb>] kick_requests+0x169/0x3cb [ceph]
[120633.443292]  [<ffffffffa009a8c1>] ceph_osdc_handle_map+0x370/0x522 [ceph]

Since we're probably screwed anyway if a small kmalloc is
failing, don't bother with trying to be clever here.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/osd_client.c

@@ -615,7 +615,6 @@ static int __map_osds(struct ceph_osd_client *osdc,
 	struct ceph_pg pgid;
 	int o = -1;
 	int err;
-	struct ceph_osd *newosd = NULL;
 
 	dout("map_osds %p tid %lld\n", req, req->r_tid);
 	err = ceph_calc_object_layout(&reqhead->layout, req->r_oid,
@@ -639,25 +638,15 @@ static int __map_osds(struct ceph_osd_client *osdc,
 	if (req->r_osd) {
 		__cancel_request(req);
 		list_del_init(&req->r_osd_item);
-		if (list_empty(&req->r_osd->o_requests)) {
-			/* try to re-use r_osd if possible */
-			newosd = get_osd(req->r_osd);
-			__remove_osd(osdc, newosd);
-		}
 		req->r_osd = NULL;
 	}
 
 	req->r_osd = __lookup_osd(osdc, o);
 	if (!req->r_osd && o >= 0) {
-		if (newosd) {
-			req->r_osd = newosd;
-			newosd = NULL;
-		} else {
-			err = -ENOMEM;
-			req->r_osd = create_osd(osdc);
-			if (!req->r_osd)
-				goto out;
-		}
+		err = -ENOMEM;
+		req->r_osd = create_osd(osdc);
+		if (!req->r_osd)
+			goto out;
 
 		dout("map_osds osd %p is osd%d\n", req->r_osd, o);
 		req->r_osd->o_osd = o;
@@ -674,8 +663,6 @@ static int __map_osds(struct ceph_osd_client *osdc,
 	err = 1;   /* osd changed */
 
 out:
-	if (newosd)
-		put_osd(newosd);
 	return err;
 }